The lysosomal storage diseases are a group of inherited enzyme deficiencies that produce fatal degenerative syndromes, most of which affect the CNS. Studies of neural stem cell transplantation and direct gene transfer in mouse disease models have shown that supplying the normal enzyme can significantly reduce pathology. However, metabolic diseases that affect the CNS typically have global lesions and gene delivery within the brain has been relatively limited, particularly in large mammals. We have shown that injection of AAV2 vectors into the parenchyma of the brain in the mouse results in localized transduction, but can mediate widespread distribution of the normal enzyme by secretion. This mediates correction of storage lesions in cells distal from the transduction site, by receptor-mediated endocytosis. We have recently found that when AAV2 is injected into the cerebral lateral ventricles in the newborn mouse brain, the vector becomes widely distributed by the CSF circulation, resulting in disseminated gene expression. In this project we will study an inherited deficiency of acidic alpha-D-mannosidase (MANB), which results in the accumulation of undegraded mannose-rich oligosaccharides in cellular lysosomes, prominently in the central nervous system (CNS), causing mental retardation and other abnormalities. We have studied the genetics, biochemistry, and pathology of a cat model of the human disease, which is maintained in a breeding colony. We will investigate the ability of AAV-transduced cells to secrete therapeutic levels of enzyme and determine the volume of brain tissue that can be corrected surrounding transduction sites. We also have shown recently that there is significant pathology that can be quantitatively evaluated in living animals by non-invasive nuclear magnetic resonance (NMR) methods. The effects of treatment will be evaluated ante-mortem by clinical neurologic assessments and MR. These findings will be compared to post-mortem analysis by histopathology, electron microscopy, and biochemical analyses. The alpha-mannosidosis cat is a model for evaluating treatment of the CNS in a large mammalian brain, with disseminated lesions, under conditions similar to those that will be encountered in treating the human disease.